When machining low and medium alloyed steels and stainless steels with cemented carbide tools, the cutting edge is worn according to different wear mechanisms, such as chemical wear, abrasive wear, and adhesive wear and by edge chipping caused by cracks formed along the cutting edge. The domination of any of the wear mechanisms is determined by the application, and is dependent on properties of the machined material, applied cutting parameters, and the properties of the tool material. In general, it is very difficult to improve all tool properties simultaneously, and commercial cemented carbide grades have usually been optimized with respect to one or few of the above mentioned wear types, and have consequently been optimized for specific application areas.
WO 2007/069973 discloses a coated cutting tool insert particularly useful for dry and wet machining, preferably milling, in low and medium alloyed steels, stainless steels, with or without raw surface zones. The insert is characterized by a WC—TaC—NbC—Co cemented carbide with a W alloyed Co-binder phase and a coating including an innermost layer of TiCxNyOz with columnar grains and a top layer at least on the rake face of a smooth α-Al2O3.
U.S. Pat. No. 5,879,823 discloses a coated cutting tool with a (Ti,Al)N-layer applied by PVD and an alumina layer applied by PVD on top of the (Ti,Al)N-layer.
U.S. Pat. No. 5,310,607 discloses a hard coating including mainly (Al,Cr)2O3 crystals and a chrome content higher than 5 at % wherein the (Al,Cr)2O3 is a single crystal. The coating is deposited at a temperature lower or equal to 500° C. The hard coating is deposited by a CVD or PVD process.
What is needed is a coated cutting tool with enhanced performance for machining of steels and stainless steels. The invention is directed to these, as well as other, important needs.